When a DC motor is initially started, a surging current will be always introduced inside the DC motor. Because the DC motor is suddenly started from the stationary state, the surging current will cause the DC motor a big mechanical shock. This mechanical shock is the main reason of the damages of the DC motor.
The conventional methods for eliminating the surging circuit of the DC motor nowadays are complicated and expensive. One of these methods is to use a protecting circuit to protect the DC motor after the surging current is introduced, but the protecting circuit will also be damaged after using for a long time. Another method is to use a circuit to start the DC motor in the way of a pulse-width modulation (PWM). However, this PWM circuit will introduce an electroacoustic sound while the DC motor is started.
Therefore, an object of the present invention is to improved the defects of the prior art.